[arch][arm-m] fix cortex-m code post SMP
[arch][arm-m] fix cortex-m code post SMP

At the top of each irq handler, make sure PRIMASK is set to 1, so
that arch_ints_disabled(), which is now used by the spinlock code,
returns the appropriate value. On Cortex-M this is not exactly the
same thing as having irqs disabled, but it's the easiest thing to
query as long as the model of only having one level of irq handler
is maintained.

littlekernel/lk,sndnvaps/lk,nvll/lk,GCrean/lk,GCrean/lk,skabet/lk,srodrig1/lk,littlekernel/lk,nvll/lk,srodrig1/lk,hollanderic/lkstuff,travisg/lk,GCrean/lk,ErikCorryGoogle/lk,littlekernel/lk,skabet/lk,nvll/lk,minglun-tsai/lk,skabet/lk,ErikCorryGoogle/lk,ErikCorryGoogle/lk,minglun-tsai/lk,srodrig1/lk,littlekernel/lk,minglun-tsai/lk,sndnvaps/lk,sndnvaps/lk,sndnvaps/lk,travisg/lk,hollanderic/lkstuff,GCrean/lk,hollanderic/lkstuff,travisg/lk,nvll/lk,minglun-tsai/lk,srodrig1/lk,GCrean/lk,ErikCorryGoogle/lk,skabet/lk,sndnvaps/lk,travisg/lk,srodrig1/lk,nvll/lk,skabet/lk,hollanderic/lkstuff